1. Field of the Invention
The invention relates to mutants and alleles of the opcA gene which encode variants of the OpcA subunit of glucose 6-phosphate dehydrogenase (EC: 1.1.1.49) and to processes for preparing amino acids, in particular L-lysine and L-tryptophan, by using bacteria which harbor said alleles.
2. Prior Art
Amino acids are applied in human medicine, in the pharmaceutical industry, in the food industry and especially in animal nutrition.
Amino acids are known to be prepared by fermentation of strains of coryneform bacteria, in particular Corynebacterium glutamicum. Due to the great importance, continuous efforts are made to improve the production processes. Said processes may be improved with respect to fermentation-related measures such as, for example, stirring and oxygen supply or the composition of the nutrient media, such as, for example, sugar concentration during the fermentation, or the working-up into product form, for example by means of ion exchange chromatography, or the intrinsic performance characteristics of the microorganism itself.
The performance characteristics of said microorganisms are improved by applying methods of mutagenesis, selection and mutant choice. This enables strains to be obtained which are resistant to antimetabolites or auxotrophic for metabolites which are of regulatory importance, and produce amino acids. A known antimetabolite is the lysine analog S-(2-aminoethyl)-L-cysteine (AEC).
For some years now, methods of recombinant DNA technology have likewise been employed in order to improve L-amino acid-producing Corynebacterium strains, by amplifying individual amino acid biosynthesis genes and studying the effect on amino acid production. A summary on a wide variety of aspects of the genetics, the metabolism and the biotechnology of Corynebacterium glutamicum can be found in Pühler (chief ed.) in Journal of Biotechnology 104 (1-3), 1-338, 2003.
Moritz et al. (European Journal of Biochemistry 267, 3442-3452 (2000)) report physiological and biochemical studies on glucose 6-phosphate dehydrogenase of Corynebacterium glutamicum. According to studies by Moritz et al., glucose 6-phosphate hydrogenase consists of a Zwf subunit and an OpcA subunit.
Moritz et al. (European Journal of Biochemistry 267, 3442-3452 (2000) describe a method of determining the enzymic activity of glucose 6-phosphate dehydrogenase.
The nucleotide sequence of the gene encoding the OpcA subunit of Corynebacterium glutamicum glucose 6-phosphate dehydrogenase is generally accessible, inter alia, in the database of the National Center for Biotechnology Information (NCBI, Bethesda, Md., USA) of the National Library of Medicine (Bethesda, Md., USA), under the number AX121828. It can furthermore be found as sequence No. 1744 in the patent application EP1108790.
Other databases such as, for example, the nucleotide sequence database of the European Molecular Biologies Laboratories (EMBL, Heidelberg, Germany and Cambridge, UK) or that of the Swiss Institute of Bioinformatics (Swissprot, Geneva, Switzerland) or that of the Protein Information Resource Database (PIR, Washington, D.C., USA) may likewise be utilized.
The microbial biosynthesis of L-amino acids in coryneform bacteria is a complex system and linked on multiple levels to various other metabolic pathways in the cell. It is therefore not possible to predict whether mutation alters the OpcA polypeptide of glucose 6-phosphate dehydrogenase in such a way that production of L-amino acids is improved. For reasons of better clarity, SEQ ID NO: 1 depicts the nucleotide sequence of the zwf gene encoding the OpcA subunit of Corynebacterium glutamicum glucose 6-phosphate dehydrogenase (“wild type gene”), according to the information of the NCBI database, and SEQ ID NO: 2 and 4 depict the amino acid sequence resulting therefrom of the encoded glucose 6-phosphate dehydrogenase. In addition, SEQ ID NO: 3 indicates nucleotide sequences located upstream and downstream.